Register Schema - Mongo Relationship

im new working with mongoDB and node.js im trying to creat a relation between two models applications and contactsapp

applicationsModel

'use strict'

const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const contactapp = mongoose.model('ContactApp');

const ApplicationsSchema = Schema({
  application_code: String,
  name: String,
  comments: String,
  version: String,
  developer: String,
  url: String,
  active: Boolean,
  press_package: String,
  pad_file: String,
  image: String,
  category: [String],
  contacts: [{ type: Schema.ObjectId, ref: "ContactApp" }]
});

module.exports = mongoose.model('Applications', ApplicationsSchema);

contactsappModel

'use strict'

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const ContactappSchema = Schema({
  fullname: String,
  avatar: String,
  company: String,
  jobTitle: String,
  email: String,
  phone: String,
  sex: String,
  country: String,
  channel: String,
  website_url: String,
  linkedin_url: String,
  xing_url: String,
  notes: String,
  active: Boolean
});

module.exports = mongoose.model('ContactApp',ContactappSchema);

but when the console give me the error Schema hasn't been registered for model "ContactApp".

via Miguel Angel Gomez